The present invention relates generally to the combustion of fuel oil, and more particularly to the atomization of fuel oil in a combustion furnace. In particular, the present invention provides improved apparatus and methods for discharging atomized fuel which provide low levels of air pollution emissions, such as oxides of nitrogen (NOx), carbon monoxide (CO), particulate matter (PM) and opacity. The present invention also provides improved durability over prior art atomizers.
For environmental and economic reasons, there is an ongoing need to improve the efficiency of fuel oil atomizers which supply fuel oil to a furnace. In particular, it is well known that “heavy” fuel oil (e.g., heavy number 6 oil or “bunker” oil), which contains organically bound nitrogen and sulfur compounds and has a high asphaltene content, is difficult to combust while producing low air polluting emissions. Particulate matter (PM) in the form of ash and unburned carbon, carbon monoxide (CO) or partially oxidized carbon, oxides of nitrogen (NOx), and opacity are in particular troublesome air emissions for many furnaces burning heavy oil. It is known that the formation of NOx can be reduced by providing fuel-rich and fuel-lean zones in the atomizing spray pattern.
Prior art atomizers, such as those disclosed in U.S. Pat. Nos. 5,860,600 and 5,826,798 to Schindler which have been assigned to Todd Combustion, Inc. (referred to herein as the “Todd patents”), are designed to provide improved emission performance. Both Todd patents comprise alleged improvements over prior art atomizers having a cup-shaped internal whirling chamber into which fuel under pressure is delivered through an array of passages or slots that are arranged tangentially to the whirling chamber. An array of discharge holes, each of which is the same radial distance from the center of the whirling chamber, provides for passage of the fuel from the whirling chamber to the furnace combustion chamber.
U.S. Pat. No. 5,826,798 discloses an atomizer design wherein the atomizer is provided with an array of discharge holes located a distance from the atomizer whirling chamber greater than 400/512 times the radius of the whirling chamber.
U.S. Pat. No. 5,860,600 discloses an atomizer design wherein the atomizer is provided with two arrays of discharge holes adjacent and offset from each other.
However, prior art atomizer designs of the type disclosed in the Todd patents and other prior art may be subject to premature wear, causing fuel pressure and fuel flow imbalances, leading to opacity excursions and increased NOx levels.
It would be advantageous to provide apparatus and methods for atomizing fuel oil which reduce NOx emissions over that obtained by the prior art, while also improving or maintaining CO, PM and opacity generation. It would be particularly advantageous to provide for such improvements in emissions while also increasing the durability of the atomizer components. The methods and apparatus of the present invention provide the above-mentioned and other advantages.